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Expression of color difference（色差的表示）

Assessment of color is vital in manufacturing and marketing of textile products. Color can be assessed either visually or by the use of instruments.Assessment consists of detemining whether a color difference exists,describing the difference ,and determining whether or not color differences are tolerable. Assessment of color differences is fraught with difficulties,and literally dozens of systems have been devised to express color difference.Some of these systems are based on some theory of color vision while others are purely empirical.The difference in location of samples in CIELAB color space is used widely in textiles to assess color differences between samples.
The difference in coordinates in the CIELAB space can be resolved into the three components to give an indication of the magnitude and direction of the color
△a*=a*1-a*2
△b*=b*1-b*2
△L*=L*1-L*2
difference between two colors,1 and 2. The sign of the difference indicates the direction of difference in Color while the magnitude of the difference indicates the size of the color difference.Total color difference, △E,is the actual distance in
△E= [(△a*)2+(△ b*)2+(△ L*)2]1/2
CIELAB color space between samples.The location of a color in CIELAB color space can also be specified in terms of coordinates L*, C*,and H*,where C*represents chroma and H* is the “hue angle.” C* is the distance between the sample and the axis and H is the angle made by the chroma line and the a* axis.
△E= [(△C*)2+(△ H*)2+(△ L*)2]1/2
The total color difference between two samples expressed in terms of chromaticity and hue angle is A color difference between two samples is ofteb expressed by the differences in hue angle, △ H,and △C,of the two samples.